1. Field of Invention
The present invention generally concerns the area of interventional radiology.
More particularly, the present invention relates to imaging methods and systems to determine the position of a medical instrument positioned inside a patient.
2. Description of Related Art
The principle of interventional radiology procedures, for a user, consists of guiding and deploying a medical instrument inside a patient, being assisted by a medical imaging system.
This medical imaging system allows real-time acquisition, processing and display of data on the position of the instrument, and a gives a representative image of inside the patient.
Medical imaging systems have already been proposed allowing the display of a three-dimensional (3D) illustration of a medical instrument in its current position and of the patient's vascular system.
Document U.S. Pat. No. 6,317,621 describes a medical imaging system comprising acquisition means, processing means and display means. The display means allow the display of a 3D representation illustrating the medical instrument in its current position and the patient's vascular system. To calculate the 3D position of the medical instrument, the processing means use two 2D images acquired simultaneously at different angles by the acquisition means.
However, the simultaneous acquisition of two 2D images requires the emission of higher X-ray doses towards the patient. These X-ray doses are harmful for the patient. Additionally, there is uncertainty regarding the calculated 3D coordinates of the medical instrument.
Document U.S. Pat. No. 6,389,104 describes a medical imaging system allowing the display of a 3D illustration of a medical instrument in its current position and the patient's vascular system. The imaging system comprises processing means able to determine the current position of the medical instrument using a single 2D image acquired by acquisition means.
One drawback with this type of method is that it cannot be applied to the determination of the 3D position of a medical instrument being navigated inside a cavity (the heart for example).
This type of method effectively can only be applied to determining the position of the tip of the medical instrument inside vessels (a vein for example) for the following reason:                A cavity has a larger volume than a vessel.        
The number of potential 3D positions of the tip of a medical instrument moved inside a cavity is therefore much higher than the number of potential 3D positions of the tip of a medical instrument being moved inside a vessel.
Methods of the type described in U.S. Pat. No. 6,389,104 cannot therefore be applied to the determination of the current 3D position of the tip of a medical instrument being guided inside a cavity on account of the fact that the number of potential 3D positions therein is too high.
Further, there is no accurate mathematical method allowing calculation of the 3D coordinates of a point using a single 2D image. Therefore, the displayed 3D representation does not represent the medical instrument in its true current position. The displayed 3D representation represents the instrument in its most probable current position. However, the operator does not have any visual information specifying the probability of the accuracy of the displayed current position.
This may lead to degradation of the patient's inner structures by the operator relying on inaccurate data for navigation of the medical instrument.
An aim of the present invention is to propose a medical imaging method and system with which to overcome at least one of the above-mentioned drawbacks.
More precisely, one purpose of the present invention is to propose a medical imaging method and system allowing the accurate tracking of the 3D position of a mobile, guidable medical instrument being navigated within a cavity.